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IRD figures show $300,000 is largest debt with $14,421 the median balance for most.

Worried about the size of your student loan? The top 10 borrowers each owes more than $300,000, new figures supplied to the Herald reveal.

Inland Revenue said the 10 borrowers with the largest loans collectively owed more than $3 million as at June 30 last year. In a response to an Official Information Act, the agency declined for privacy reasons to provide details including how much each person owed, whether they lived overseas, and how long they had held a loan.

An IRD spokesman said there were a number of methods used to target borrowers in default.

"Action based on the amount of default is just one. We endeavour to contact all of our borrowers who are in default, however, our success can be hindered by those who do not provide us with their latest contact information. To combat this we work closely with collection agencies in Australia and the UK who work with borrowers to get them back on track with their obligations."

Last month Ngatokotoru Puna, 40, was arrested at Auckland Airport over a student loan in default as he tried to return home to the Cook Islands.

Puna has lived in the Cooks for 13 years in which time his $40,000 loan ballooned to about $130,000. He borrowed $5000 from his parents to pay the IRD before the court was satisfied he could leave the country.

The arrest policy, passed in March 2014, is the harshest in a range of measures to recoup debt from the 110,600 borrowers living overseas.

Last year those based overseas made up 15 per cent of all borrowers, but 74 per cent of borrowers with overdue payments, and had 90 per cent of the amount overdue.

There were 5735 borrowers who each owed more than $100,000 last year. However, most people owe much less - the median loan balance in 2014 was $14,421.

A key enforcement measure will come into force this year in the form of an information-sharing agreement with Australia, which will allow for the exchange of contact details of Kiwi borrowers living in Australia. That could see thousands more borrowers receiving warning notices.

The cost of tertiary education has become a major political issue, after Labour leader Andrew Little used his State of the Nation address last month to announce a multi-billion dollar plan to provide every New Zealander with three years of free tertiary education.

It will provide three years of free post-school education over a person's lifetime and can be used for any training, apprenticeship or higher education approved by NZQA.

On Wednesday, Mr Little went after Prime Minister John Key on the issue, arguing that the home ownership rate among Kiwis under 40 had more than halved since student loans were introduced.

Mr Key responded by saying New Zealand was the only country in the world with zero-interest student loans, and the 70-80 per cent subsidisation of the full cost of each student's tertiary education by the Government was about right.